The present invention relates to the isolation and/or identification of highly pure mesenchymal stem cells by means of a novel cell surface marker, and the use of this cell surface marker and the isolated stem cells.
Mesenchymal stem cells (MSC), also called mesenchymal stromal cells, are pluripotent cells which possess the ability, under suitable in vitro and in vivo conditions, to differentiate into various mesenchymal tissues. Thus they can for example differentiate into osteocytes, chondrocytes, adipocytes and myocytes, and form bone, cartilage, adipose and muscle tissue. In addition, however, they can also differentiate into astrocytes, neurons, endothelial cells, hepatocytes, pancreas-like cells and pulmonary epithelial cells. Morphologically, they can be recognized by their fibroblastoid phenotype, and can be found in various human adult and embryonic tissues, including the brain, bone marrow, umbilical blood, in blood vessels, in the skeletal muscle, skin, liver, gums and the placenta.
MSC from bone marrow express a range of surface markers such as for example CD105 (endoglin, SH2), CD73 (ecto-5′-nucleotidase, SH3, SH4), CD166 (ALCAM), CD29 (β1-integrin), CD44 (H-CAM) and CD90 (Thy-1), which are to some extent also found on endothelial and epithelial cells and on muscle cells. However, MSC can be distinguished from hematopoietic stem cells since MSC do not express the markers CD45, CD34 and CD133 specific for hematopoietic stem cells.
MSC have the property of rapidly and stably adhering on plastic or glass surfaces and forming fibroblast colonies (“colony-forming units fibroblast” (CFU-F)). However, the latter are heterogenous as regards their proliferation and differentiation capabilities.
MSC with a defined differentiation potential are of great interest in medicine and research. They can in particular be obtained from the bone marrow, even from that of older people, have a high division rate and can as stated differentiate into tissue cells of mesenchymal origin. They could therefore be used directly for example in the context of stem cell therapies for the treatment of degenerative diseases of organs such as bone, cartilage, tendons, muscle, connective tissue, blood cells, etc.
For the obtention or isolation of MSC, unfractionated bone marrow cells are at present used as the starting material. In culture bottles, as well as MSC, other cells such as macrophages and endothelial cells also adhere. After defined periods, the non-adhering cells (mostly hematopoietic cells) from the sample are discarded. However the cells obtained in this manner are poorly defined and differentiate not only into heterogenous MSC populations, but also into osteoblasts and/or into osteoblast precursor cells, adipose cells, reticular cells, macrophages and endothelial cells. Hence specific treatment of degenerative diseases of an organ with MSC with no defined differentiation potential is difficult, or problematic because of possible side effects.
Hitherto, the isolation of especially pure MSC, both from primary tissue and also from cultured MSC was not possible or known according to the prior state of the art, but would offer the advantage of specifically using stem cells thus identified for the therapy/treatment of diseased, degenerated or damaged tissue into which the stem cells thus specifically isolated differentiate.
Thus for example cartilage injuries could be treated by introducing specifically isolated mesenchymal stem cells with chondrogenic differentiation potential either directly in situ into the affected tissue, where they differentiate into chondrocytes and thereby replace the damaged tissue (stem cell therapy). On the other hand, however, differentiation into chondrocytes in vitro can also be of interest if differentiated chondrocytes are to be isolated, for example for research/diagnosis/medicine.
Against this background, an object of the present invention is to provide novel ways whereby especially pure mesenchymal stem cell populations can be isolated.